The presence of harmful chlorinated substances in the subsurface    
is a large threat to our groundwater reserves. Fortunately, nature    
has found several ways to destroy these compounds. In the subsurface,    
both biological and chemical processes may occur that cause    
degradation to non-toxic end products. This is called natural attenuation    
or NA. Some of these NA processes are well-known and    
can be demonstrated rather easily. For other processes that can potentially    
play an important role, it is more difficult to find evidence.    
Traditional methods are not suited for demonstrating these processes    
and their significance in the subsurface is still unknown.    
    
In this project, we investigate the use of a new analytical technique    
called “compound specific stable isotope analysis (CSIA)” to study    
the relevance of the abovementioned NA processes. With CSIA, we    
can study the properties of single atoms in the contaminant molecules.    
Chlorinated solvents consist of carbon and chlorine. By looking    
into both types of atoms, it is possible to identify and quantify    
different NA processes. CSIA for carbon is already applicable for    
field application, but CSIA for chlorine has been developed very recently    
and requires optimization.    
    
The objective of the project is to optimize the use of CSIA for chlorine    
and to demonstrate the use of combined carbon and chlorine    
isotope analysis at tool for demonstrating natural attenuation of    
chlorinated solvents.